Last one for night - unintentional torture test of variable focus


#1

I can’t remember if @Dan said that variable focus is fully functional but I just tested it big time…

So went to simply engrave my division’s logo, and figured a good time to figure out how to invert something with a boolean difference in AI. So nailed that down and decided to do a deep engrave with the letters standing out in proof grade maple. Selected the 2nd from darkest for the engrave settings.

Um, who here (who isn’t a laser user already) knew that wood curls like plastic when it gets hot?? Really? And once curled proceeds to move around in the air-assist blast as the head goes over it? And that variable focus seems to actually track all of that???

But whose laser cutter adapted to all of that and did a perfect engrave? THIS GUY!

I have decided that since we are a technical research division, I am saying I did this deliberately like those silly curved LG sets…


Weekly Highlights for the Week ending April 8th, 2017
#2

If it has that capability enabled it isn’t something I have noticed. Would be cool.


#3

Was the cut done before the engrave?

Would pausing after the engrave, before doing the cut allow cooling to prevent wood warp-age?

Would that apply to acrylic (engrave, cool , cut)?


#4

It does cuts first by default. This is an issue on acrylics as well. I try to cut last if im doing an engrave on 1/8.


#5

At the risk of a flag, but O so appropriate:


#6

I thought about that, but if you look at the piece of wood, it was the remainder of a piece, so there was maybe 1/4" around the sides, so likely would have curled around anyway.

That’s what this was a test for. Having been burned by curling acrylic (ha, see what I did there) when acrylic curled on me in Clifford I figured hey, let’s try this in wood first…

Now any experts out there on acrylic know, if I do this kind of thing on acrylic, can I hold down the edges firmly (say strong neodymium magnets) and prevent this?

Also @Dan, can I set a precise depth to engrave down to? I need to go down 0.5mm (it’s a cool project that I need an insanely precise mold for).


#7

:raised_hand:

It’s a problem in the wood industry. It has to do mostly with moisture, and also the grain in solid wood, or internal stresses in sheet goods. When you plane or remove a lot of surface from solid, it curls ultimately , because the core will have more moisture but the side that isn’t planed is dryer. So typically to counter this you plane both sides more less equally. I think the heat of the laser and depth of cut speed it up. Also when veneering anything you have to put a layer on the back as thick as the front face layer, to balance the drying of the back. It’s why all plywoods are odd number layered(ok technically there is 2 ply plywood but it’s super thin…).

Also with any sheet good there is internal stresses from all the pressure they put on the core materials(substrate). If you ever rip a 4x8 of 2 side melamine on particleboard along the long side, if you wait a minute or by the end of the cut, it will actually curve to the left or right(but not the same as a banana cut, that’s another story). I’ve seen that in a 2 foot wide piece, which is very annoying for cabinet construction.

So heat plus exposing moisture to the air, and heating said moisture will lead to curling. As said above, try the engrave first, and hope that the larger piece can remain flat before cutting.


#8

Thats really sharp!


#9

Huh! Well sorry @Rita , I guess I didn’t need to report that.

(Newbies!) :stuck_out_tongue_winking_eye:

I learned it about six weeks ago with my first cuts. It’s so humid around here that if you take too much of the material out of one side, it starts to curl. (Non-PG material was a heck of a lot worse though.)

I’m still trying to figure out a way around it for single sided cuts. Shallower engraves help, as do double sided engraving. (The latter completely eliminates the problem…those rack hooks with two-sided engraving are perfectly flat.)

What doesn’t help at all is trying to weight it down for a couple weeks to flatten it out.


#10

Actually I disagree. You did need to report it, as did I, since apparently in answer to my question of “who knew?” the answer was @jordanloshinsky, but not you and me. So, this is a documentation issue, not a technical issue (unless @Dan has some secret sauce somewhere where he can vary the depth slightly to prevent curling?) but definitely put in the manual for understanding engraving.


#11

That’s exactly what we use to do at a company I use to work at. We did a 1 piece door out of MDF. We would CNC out the interior profiles and a really big pocket on the front of the door. Most other companies will use a melamine back and hope that the hinges and paint would keep the door straight, but it doesn’t really. We were to high end to have any defects like that(easily miffed customers at our price point). So we would on a 22mm thick door mill out 7-13 mm out the front and 2-3 mm out the back as a single pocket. It created the relief you described @Jules with your 2side engrave. So that may be something people need to think about with deep engraves that will not have a piece inlaided into it.

Keep up the research guys, let’s help make some awesome machines! Thank you for trouble shooting for us all!


#12

And thanks for teaching us!


#13

To fix this piece, mist the concave side with water, wait for a second or two, then place on a hard flat surface. With the engrave side protected with several paper towels to cushion and help dry it, place a heavy flat object on top and wait until it dries. The sign should be flatter as the water makes the wood fibers swell.

Ps. Loving all your posts, thank you!


Tips For the Inexperienced
#14

I’m going to try this on the hedghog trivet - it’s still a little warped.


#15

Belongs in the “Tips” thread.


#16

Son-of -a-Gun! Almost instantaneous straightening! (Possibly because there were tiny pinholes in the back facing from the (“known issue”) overburn on the corner points from the deep score.

That is one heck of a tip!


#17

This also for veneers. If you veneer the front of an object, then for best flatness you need to veneer the back as well (unless you have fortuitously matched the expansion rates of the veneer and main material).


#18

So maybe a spritz of water before engraving would help? Or would that make it bow upwards and defeat the purpose?


#19

Excellent! Thank you for the tip!


#20

That is awesome!